1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and in particular to a method of manufacturing a semiconductor device having a semiconductor layer.
2. Description of the Background Art
Conventionally, liquid crystal displays (LCDs) include a display pixel portion arranged in a matrix and a drive circuit portion which drives the display pixel portion. Generally, for LCDs, a transistor which configures the drive circuit portion is required to have higher mobility (rapidity) than a transistor which configures the display pixel portion. In recent years, high mobility has been achieved to some extent by employing polycrystalline silicon film as an active layer of a thin film transistor (TFT) which configures the drive circuit. Thus, the TFT formed of polycrystalline silicon film has been employed as not only a transistor configuring the display pixel portion but also a transistor configuring the drive circuit portion. As polycrystalline silicon film has been used as the active layers of a TFT configuring the display pixel portion and the TFT configuring the drive circuit portion, a so-called LCD integral with a drive circuit has been developed in which the display pixel portion and the drive circuit portion are formed on the same substrate.
For LCDs including such a TFT that employs polycrystalline silicon film as an active layer, a further rapid TFT configuring the drive circuit portion is required with higher definition and higher density of the pixels of the LCDS. Accordingly, researches have been conventionally conducted to improve the mobility of the TFT active layer formed of polycrystalline silicon film. Various methods have been proposed to achieve high mobility, for example, by changing a material gas used in forming a silicon layer serving as a polycrystalline silicon film from silane (SiH.sub.4) gas to disilane (Si.sub.2 H.sub.6) gas to relatively increase the grain size of the polycrystalline silicon film after its solid phase crystallization (SPC).
However, it is difficult to obtain a TFT active layer of sufficient high mobility even with such a technique proposed as above. Thus, it is particularly difficult to achieve a faster drive circuit when such a TFT is used in an LCD and hence to improve the display characteristics of the LCD.